AU1 V8 , sometimes runs on 7!

[trimmaster]

Does anyone know what could be causing the problem to make my V8 run on 7 or less whenever it feels like it.
Yes, I've changed plugs and leeds and even removed the metal boots where they plug onto the plugs as advised by an ex Tickford engineer. ( to eliminate cross firing).
The problem has ocurred at so many different times that I can't get any history to work it out.
It has done it on start up in winter, turn it off, start it again and is perfect and sometimes still missing. Same in summer, so it's not a hot or cold thing.
It has done it while driving around town at low speeds and also while cruising on the freeway, as was the case on Saturday on the Citylink in Melb. ( for those of you who saw the Blue T series sitting for 2 1/2 hrs with the hazard lights on, only to be told when the RACV guy did finally turn up that I should buy a, well you can guess!! NOT HAPPY! And he didnt even help.
Its been back to the dealers a few times, but it never does it then, and of course it never logs a fault code.
Only thing left to change are coil packs, but at the current price I'm not so keen without some proof. Am I missing another sensor?
Occasionally I do press the economy switch but this is rediculous.
Any suggestions? I'd also like to hear from fellow AU1 V8 owners.